I've been having this problem for the past month. I will be listening to my "Likes" list and after playing through a number of songs continuously it will randomly jump back to a random song. So for example, if I've been listening to tracks from 20 through 30, after it's done playing track 30 it will then jump back and play track 3 or track 6 or track 1.
This is really frustrating because since Sound Cloud has gotten rid of the very nice feature of being able to jump to your current track by clicking on the track name on the bottom toolbar, I now have to scroll through numerous pages to get back to where I left off. Then this whole thing will happen again...
P.S. this is not specifically a "playlist" problem, there just isn't another option in the "sub forum" menu.